Rheostat



A. B. CADMAN Jan. 4, 1938.

RHEOSTAT 2 Sheets-Sheet 1 Filed March 9, 1935 TTORNEYS INVENTOR uqddi B. Cam man CMAQ P Jan. 4, 1938. A. B. CADMAN 0 RHEOSTAT Filed March 9, 1935 2 Sheets-Sheet 2 c INVENTOR 0446/1; B. Cad/nah pu cuhfgm relative motion of thetwo Patented Jan. 4, 1938 UNIT D STATES PATENT. OFFICE This invention relates to rheostats for regulating the flow of electric current, and has for its Another object of the invention is to provide an improved rheostat in which the full regulatory range thereof through a large number of incremental steps is covered by a small relative motion of the coacting parts.

A further object of the invention is to provide an improved rheostat in which the resistance unit are mounted for ready removability and interchangeability so that any desired resistance range may be obtained bycombination of elements and incorporation thereof in the rheostat structure.

Another object is to provide an improved rheostat comprising a resistanc unit and a contactor unit mounted for relative movement wherein the separate resistance elements are mountedin spaced groups and a plurality of contacting degroups of resistance elements to coact therewith; the arrangement beingsuch that upon units the contact .devices are progressively carried into coaction with the elements of each group and are successively brought into association with the respective groups of resistance elements whereby a wid'e range of current variation through small incremental steps is accomplished by a small relative movement of the two units. &

Other objects and advantages of, the invention will become apparent from the following detailed description of a preferred embodiment ,thereof taken in connection with the accompanying drawings, in which: 1 Figure l is an elevational view, partly in section, of a rheostat embodying the features of the invention.

Fig. 2 is a sectional view of along the line 22 of Fig. 1.

Fig. 3 is a partial sectional .view of one of the resistance elements.

Fig. 4 is a fragmentary view partly in section, taken on the line 4-4 of Fig. 2 and showing the manner in which the resistance elements are alined in their supporting disk.

Fig. 5 is an elevationaLview-taken on the line 5 5-5 of Fig. 2 with the casing shown in section.

'sistance elements are movable, each preferably comprises a therrheostat taken held together by screws [8 Fig. 6 is a sectional view taken on the line 6-8 of Fig. 5.

Fig. 7 is a sectional view taken along the line Figs. 8 to 1 2,inclusive, are views showing the 5 relative positions of the contact arms and the is to be understood that I do not thereby intend to limit the invention to the specific form dis- 1 closed, but intend to cover all modifications and alternative constructions falling within the spirit and scope of the invention as expressed in the appended claims.

The rhecstat shown in the drawings for purposes of illustration is of the parallel resistance type having a resistance unit and a contact mechanism mounted for relative rotary movement. Generally stated, the resistance unit comprises a supporting member upon which individual remounted with one of their 25 individual yielding movement and grouped in a plurality of rows. To render the resistance elements readily interchangeable and quickly rerigid rod carrying one of said contacts at one end. I

The contact mechanism which preferably is the rods i3 removably mounted in parallel apertures 45 formed in a stationary. supporting member" I (Fig, 2) comprising two plates I5 and I6 of in sulating material such as bakelite and spaced apart by projecting pads I! -(Fig. 7) which are 5 threading into tapped holes in the pads on theplate IS.

The plates are formed with coaxially alined apertures l8 arranged in substantially radially disposed, angularly spaced rows A, B, C, D, E,

in the present es having their intersecting at unit, but progressively spaced from each other as shown in Fig. 4. p

The apertures in the plate I5 are closed at one end by a segmental contact member 20 (Figs. 2 and 5) secured tightly against the outer face of the plate by the screws I8 which hold plates I5 and I6 together and by a bolt'2I (Figs. 5 and 6) which extends through the plate I5 and the member. A nut 22 threaded on the bolt 2I engages the member 20 and provides an electrical connection between the memberand the bolt, the latter serving as one binding terminal of the rheostat.

The individual resistance elements I3 disposed in the apertures are electrically connected with the member 20 through the compression springs 23, thereby making the elements electrically common at one end. The springs are so proportioned that they urge the resistance elements into contact with the face of a contact mechanism 24 which abuts against the outer face of the plate I6.

The resistance elements I3 (Fig. 3) comprise rods of resistance material such as compressed carbon having ends over which are pressed metallic cups I3 which serve minals or wear-resisting contacts for the elements. Being entirely independent of each other and removably mounted, the resistance elements I3 may be constructed to have various resistance values and adapted for ready interchangeability whereby the current regulating characteristics of the rheostat may be altered to suit the particular requirements of different circuits.

To provide a second terminal for the rheostat, the plates I5 and I6 of the resistance unit are provided with an additional pair of axially alined apertures 25 (Fig. 6) which are located between the rows B and C and somewhat closer to the latter row. Within metallic rod 26 electrically connected by a pigtail conductor 21 with a segmental conductive plate 28 secured to the outer face of the plate I5. A spring 29 bearing against the plate 28 urges the rod into engagement with the face of the contact mechanism 24. The segment 28 is secured to the plate I5 by one of the screws l8 whichhold the plates I5 and I6 together and by a bolt 30 which extends through the plate and segment. Anut 3| threaded on the bolt 30 tightly engages the segment and provides an electrical connection between the segment and the bolt which constitutes the second binding terminal for the rheostat.

The plates I5 and I6 which constitute the supporting frame of resistance unit of the rheostat are held against rotation in a cylindrical casing 32 by bars 33 (Fig. 5) attached to the internal wall of the casing and entering segmental slots 33 (Fig. 8) in the peripheral edges of the plates. The unit is further secured to the casing by the bolts 2I and 30 which extend through holes in a cover plate 34 and are insulated therefrom by insulating bushings 31 (Figs. 2 and 6). The cover plate is detachably secured to the casing by nuts 39 threaded onto the ends of the bars 33 which project through apertures in the cover.

Coacting with the stationary resistance unit tioned that, in the slight clearance.

as connecting tera are contacted. this aperture is mounted a.

above dscribed, is the rotatable contact mechanism 24 disposed within the casing 32 in engagement with the face of the plate l6 and the contacts I3 on the ends of the resistance elements I3. The contact mechanism comprises, in the present instance, a metallic contact member 48 (Figs. 2, 6, and 8) set into the face of a support of suitable insulating maof the member 40 is flush with the surface of the disk and segmental armsor sectors 42, 43, and 44 project radially from a central hub. The arms are so propornormal open circuit position of the contact mechanism (Fig. 1), the arm 42 will just fit between the rows of elements A and F and out of contact therewith. At the same time, arm 43 will be disposed between the rows B and C with its leading edge separated from the innermost element of row C by a space equal to the width of a resistance element plus a slight clearance. The arm 44 normally lies between rows D and E and its leading edge is separated from the innermost element of row E by a space equal to twice the width of a resistance plus-a Each of the arms is wide enough to maintain .ciated.

In order to provide for contacting theindividual resistance elements one by one incidental to small incremental steps in the rotation of the contact mechanism, the leading edges of the contact arms 42, 43 and 44 are formed in planes inclined with respect to the rows of contacts. In the present instance, the contact rows are inclined with respect to the radii of their supporting disks and, since the contact member is axially alined with the disks, the leading edges of the arms may be disposed substantially radially. The edges of the arms thus approach the respective contact rows at an angle such that the elements of each row are contacted in succession.

The angular spacing of the contact rows is such that all of the elements of one row are contacted and then the elements of the next alternate row Thus, the elements of row A are first contacted successively by the arm 42 and then the elements of row C are contacted successively by the arm 43. 7 Next the elements of row E are contacted successively by the arm 44 followed by engagement of the arm 42 with the successive elements of row B and engagement of the elements of row D by the arm'43, the elements of row F being finally contacted successively by the arm 44. In this manner a difierent resistance element is contacted in response to each movement of the contact mechanism through a small angle until all of connected in circuit. In the illustrative embodiment of the invention, all of the resistance elements are connected in the circuit incidental to the contact mechanism rotating through an angle of approximately forty-five degrees.

The contact mechanism 24 is rotated by means of an operating member or link 45 (Fig. 1) cperatively connected with a mechanism supporting shaft 46 by a lever arm 41. The shaft is suitably journaled at one end in the stationary plates I5 and I6 of the resistance unit and is provided with a square shoulder 48 (Fig. 2) intermediate its ends which engages a square hole in the disk 4 I'of the contact mechanism. A collar 49 formed integral with the square shoulder 48 and at one end thereof bears against a shoulder-formed on the disk M and, in cooperation with a washer 58 contact with'all of the ele-- the elements have been tion of the mechanism is defined by shoulders 56 and 51 (Fig. l) engaging the bars 33 on the inner wall of the casing.

In operation, the rheostat is connected in a cir cult to be controlled by attaching the circuit conductors to the respective terminals 2! and 30. The circuit will be open at the rheostat with the same in normal condition as shown in Fig. 1 since the various contact blades 42, 43, and 44 will be out of contact with their elements.

To eifect the initial closure of the circuit, the link 45 is shifted slightly to the left as shown in Fig. 1 which rotates the contact mechanism 24 ment l3 therefrom.

in a clockwise direction. This rotation of the mechanism first brings the blade 42 into engagement with the innermost element l3 of the row A thereby completing the circuit through this element. The portion of the circuit within the rheostat then extends from the terminal 2|, conductive segment 20, spring 23 and resistance element I3 in the innermost position of row A, blade 42 of the contact member, contact member 40, blade 43, contact rod 26, conductive segment 28 to the terminal 30. The circuit has its maximum resistance. value under these conditions as only one of the resistance elements is included therein.

The circuit resistance will be progressively decreased in small steps as the .continued rotation of the contact mechanism 24 brings the contact arms into contact with theresistance elements l3' successively and connects these elements in parallel with the first element 13 of row A. The circult will have its minimum resistance value when the contact mechanism reaches its limiting position and all of the elements l3 are connected in parallel inthe circuit.

The circuit is restored to its normal open posisition by the shifting of the link 45 to the right as viewed in Fig. I. The-contact mechanism is rotated in a clockwise direction and the resistance elements are successively disengaged from the contact arms. Thus, the circuit resistance is increased in small steps until it reaches a condition of maximum resistance aiter which it is opened by the disconnection of the last resistance elecontact device for subsequently connecting said associated resistance resistance unit and arranged in meansincluding a contact device contactcr mechanism and mov- 2. A rheostat comprising, in combination, a resistance unit and a cooperating contactor mechanism mounted for movement relative to each other, a plurality of separate resistance elements carried by said resistance unit and arranged in spaced groups, means including a contact device carried by said contactor mechanism and movable into contact with said resistance elements in one of said groups for progressively connecting the same in common circuit relation in response to a predetermined relative movement between said unit and said mechanism, and means ineluding a second contact device carried by said contactor mechanism in spaced relation to said first named contact device for subsequently connecting said resistance elements of another of said groups progressively in common circuit relation with said first named group in response to further relative movement in the same sense between said 'unit and said mechanism but only after the first named contact device has been progressively moved into contact with all of the resistance elements in said first named group.

3. A rheostat comprising, in combination, a resistance unit and a cooperating contactor mechanism mounted for movement relative to each other, a plurality of individually, removable resistance elements'yieldably supported in said resistance unit and arranged in spaced rows, means including a contact device carried by said contactor mechanism and movable into contact with said resistance elements in one of said rows for connecting the same in common circuit relation in response to a predetermined relative movement between'said unit and said mechanism, and means including a second contact device carried 'by said contactor mechanism in spaced relation to said first named contact device, for subsequently connecting said resistance ele-' tact device has been moved .into contact with all of the resistance elements in said first named row.

4. A rheostat comprising, in combination, a resistance unit and a contactor unit having opposed surfaces mounted for movement in such planes relative to each other, a plurality of removable resistance elements carried by said resistance unit and arranged in spaced groups on said surface thereof, the elements in each group being arranged in a line, and a contactor devicemounted onv said surface of said contactor unit and in a position to be brought into electrical contact with said group of resistance elements, said contactor device having an edge lying in a plane parallel to said surfaces and inclined with respect to said group whereby the resistance elements in one group will be successively connected by a small relative movement between said contactor device and said resistance unit.

ADDI B. CADMAN.

disposed in parallel-planes and 

